The present study has two goals related to characterization of rabbit MHC (RLA) antigens. The first is to utilize animals with known RLA types in order to study linkage of immune responses to the MHC and the second is to complete the characterization of the rabbit MHC. In the study on immune responsiveness the rabbit is being examined as a possible model to examine responses against HIV-1 infection and HIV-1 immunization. Peptides and proteins from the virus were used as immunogens and both cellular and humoral responses to these were monitored. Virus neutralizing titers of sera from animals given various immunogens is determined and the immunized are then challenged with human cells infected with HIV-1 and their infection status and immune responses monitored. In the second aim of this study, a complete physical map of the rabbit MHC is being sought. Genes have been localized and ordered by pulse field gel electrophoresis (PFGE) in the class II and class III RLA regions. Thus far, the map is similar to that reported for the human HLA complex with few exceptions. Linkage studies as well as PFGE analysis have shown that genes for 21 hydroxylase, complement component C4 and tumor necrosis factor are linked in the rabbit MHC in a manner similar to that found for humans. However, certain genes that are duplicated in humans are present only in a single copy in the rabbit. Some genes recently localized to the MHC such as the heat shock protein 70 genes, are being cloned for the rabbit and probes developed in order to map these genes within the RLA complex.